On 10 March 1906, the Emperor Meiji granted Prince Yasuhiko the title Asaka-no-miya and authorization to begin a new branch of the imperial family. On 6 May 1909, Prince Asaka married Nobuko, Princess Fumi (7 August 1891 – 3 November 1933), the eighth daughter of Emperor Meiji. Prince and Princess Asaka had four children:

Like the other imperial princes of the Meiji period, it was expected that Prince Yasuhiko would pursue a career in the military. He received his early education at the Gakushūin Peers' School and the Central Military Preparatory School, before graduating from the Imperial Japanese Army Academy on 27 May 1908. Commissioned a second lieutenant of infantry on 25 December, Prince Asaka was promoted to lieutenant in December 1910, captain in August 1913, major in July 1918, and lieutenant-colonel in August 1922.

Princess Asaka traveled to France to nurse her husband. Prince and Princess Asaka also visited the United States in 1925. During that period, Prince and Princess Asaka became enthralled with the Art Deco movement. Upon returning to Japan in 1925, Prince Asaka had a new mansion built in the Art Deco style in Tokyo's Shirokanedai neighborhood. The house was completed in May 1933, but Princess Asaka died a few months later.

In November 1937, Prince Asaka became temporary commander of the Japanese forces outside Nanking (or Nanjing), then capital of China, because General Matsui was ill. As temporary commander of the final assault on Nanking between 2 and 6 December 1937, he allegedly issued the order to "kill all captives", thus providing official sanction for what became known as the "Nanking Massacre" or the "Rape of Nanking" (12 December 1937 – 10 February 1938).[2][3] The order may have actually been issued, without the Prince's knowledge or assent, by Lieutenant ColonelIsamu Chō. He was a known radical ultra-nationalist staff member of the Central China Area Army who may have released the order under the sign manual of Asaka.[4]

While Prince Asaka's responsibility for the Nanking Massacre remains a matter of debate, the sanction for the massacre and the crimes committed during the invasion of China might ultimately be found in the ratification, made on 5 August 1937 by Emperor Hirohito, of the proposition of the Japanese army to remove the constraints of international law on the treatment of Chinese prisoners.[5]

In February 1938, both Prince Asaka and General Matsui were recalled to Japan. Matsui went into virtual retirement, but Prince Asaka remained on the Supreme War Council until the end of the war in August 1945. He was promoted to the rank of general in August 1939 but held no further military commands. In 1944, he colluded with Prince Higashikuni, his nephew Prince Takamatsu, and former Prime Minister Fumimaro Konoe (1895–1945) to oust the Hideki Tojo cabinet.[2]

The former prince, Asaka Yasuhiko, moved to Atami, on the Izu Peninsula south of Tokyo. Asaka converted to Roman Catholicism on 18 December 1951, and was the first member of the Imperial Family to do so.[6] He spent most of his time playing golf. He also took an active interest in golf course development, and in the 1950s was the architect of the Plateau Golf Course at the Dai-Hakone Country Club. Asaka Yasuhiko died of natural causes on 13 April 1981 at his home in Atami, Shizuoka prefecture. He was 93 years old.